This invention relates to a magnetic head for recording and reproducing information on magnetic media.
As is well known, a magnetic head using an alloy core which is low in specific resistance is susceptible to eddy current loss which lowers its high frequency characteristics.
In the case of an alloy plate with a specific resistance p as shown in FIG. 1, the eddy current loss We per unit volume is given by We=.pi..sup.2 h.sup.2 f.sup.2 Bm/6.rho. . . . (1), where h is the thickness of the alloy plate, f is the frequency of a recording signal, and Bm is the maximum flux density. Equation (1) is explained by the fact that the skin effect of a flux produced by a high frequency eddy current causes the magnetic permeability .mu. to be substantially reduced. That is, at an audio frequency of about 10 kHz or more the magnetic permeability .mu. of an alloy core falls below that of a ferrite core as shown in FIG. 2.
In an effort to solve this problem a conventional magnetic head having an alloy core has been made of a core plate whose thickness, namely h in equation (1), is made as small or as thin as possible. To meet this requirement, an alloy magnetic head as shown in FIG. 3 has been developed, which comprises a main core 1, two sub cores 2 sandwiching the main core, and two reinforcing glass plates 3 disposed on the magnetic tape abutting face of the sub cores, in which the main core 1 is made of alloy while the sub cores 2 are made of ferrite. The main core and the sub cores are respectively provided with a winding groove 4. The alloy magnetic head constructed as shown in FIG. 3 is not free from problems, however, as its manufacturing process is complicated and the number of processing steps result in a low productivity. Namely, a number of technical problems must be solved including how to obtain appropriate flatness levels, bonding intensity and accuracy, together with avoiding bending during the assembly of the main core and sub cores. The productivity is further reduced because of the process in which micro chips of the main core and sub cores have to be bonded to each other.
Another conventional magnetic head with a ferrite core is shown in FIG. 4, which has improved productivity. Such head comprises a main core 5 made of ferrite with a winding groove 4, and two reinforcing glass members 3; FIG. 5 shows the steps involved in its production. In step (1) a core block is cut out from a ferrite material. In step (2) a plurality of head gap defining grooves, spaced apart by a distance equal to the track width Tw, are formed in the core block and thereafter the reinforcing glass members 3 are deposited in the grooves. In step (3) the winding groove 4 is formed in the core block, and the head gap face of the block is polished. In step (4) a gap material of SiO.sub.2 is sputtered onto the head gap face. In step (5) two core blocks are secured together by glass deposition so that the two gap faces confront each other. In step (6) a composite body made up of the two core blocks is cut to provide a plurality of head chips at an appropriate azimuth angle. The shadowed portions in the figure depict cut off areas. In step (7) a head chip is mounted on a circuit board, its face confronting the magnetic recording media is polished, and the coil is wound. A ferrite magnetic head thus constructed as shown in FIGS. 4 and 5 is still not free from problems, however, in that its saturation flux density is low.